Key Door

Chronological information
First game	Super Mario Bros. 2 (1988)
Latest game	Super Mario 3D All-Stars (2020)

Key Doors are doors that cannot be unlocked without the use of a key. Locked Doors usually have the appearance of a regular Warp Door with a hole.

In Super Mario series

Super Mario Bros. 2

Key Doors make their first appearance in Super Mario Bros. 2, first debut in World 1-2. The Key Door can only be opened by Keys. If the player collects an key for a Key Door, the Phanto will chase the player.

Super Mario 64 / Super Mario 64 DS

The keys in Super Mario 64 are used to open the doors that lead to the courses of the game, and in the DS remake, Key Doors that hold Mario, Luigi, Wario, and an secret Power Star.

Super Mario Advance 4: Super Mario Bros. 3

While Key Doors did not appear in Super Mario Bros. 3, but they appeared in the Game Boy Advance remake Super Mario Advance 4: Super Mario Bros. 3, in the World-e-exclusive level Doors o' Plenty.

Super Mario Galaxy

Key Doors did appear in the Ghostly Galaxy in Super Mario Galaxy, where they automatically open as soon as Mario or Luigi obtains a key. In the case of the "Matter Splatter Mansion" mission, multiple doors can be not locked at one time with single key.

Super Mario Maker series

Key Doors were introduced in Super Mario Maker in the version 1.40 update, and available at the start in Super Mario Maker for Nintendo 3DS. The key doors can be shaking a P Warp Door which shaking a Warp Door). The key doors also appear in Super Mario Maker 2, behaving as in the previous game. As of version 3.0.0 of Super Mario Maker 2, Cursed Keys can also be used to unlock the doors.

Super Mario Run

Key Doors reappear in Boohind Lock and Key, where the doors can only be unlocked with keys. Once it is opened, Key Doors did not open again. They take after the doors of the Ghost House from New Super Mario Bros. U, but with a peephole in the base.

In Captain Toad: Treasure Tracker

Key Doors reappear again in Captain Toad: Treasure Tracker, similar in previous Super Mario games.